Genetic influence on the variance in coincidence timing and its covariancewith IQ: A twin study

Performance measures on a coincidence timing task have previously been asso ciated with psychometric IQ suggesting that the ability of an individual to devote processing resources at the required time may account for some of i ntelligence test variance. Using the twin design, this study investigates w hether genetic variability explains some of the variance in coincidence tim ing and whether common genetic factors account for the association with int ellectual functioning. Fifty-five 16-year old twin pairs (28 MZ, 27 DZ) wer e tested. Individual differences in number of hits (HITS), mean absolute er ror (MAE), and intra-individual trial-to-trial consistency (SD) were signif icantly influenced by genetic factors, accounting for approximately 50 perc ent of the variance. The correlation between coincidence timing and psychom etric IQ was confirmed and ranged from 0.11 to 0.53 with a mean correlation of 0.33. In the limited sample, the correlation between IQ and the coincid ence timing measures appeared to be mediated largely by a unique environmen tal factor, with only a small loading of SD on the genetic factor influenci ng IQ. However, as the confidence intervals in the other genetic cross load ings are large, we cannot exclude the possibility of a much stronger geneti c influence.